The present invention relates to a facility for detecting and converting dial information and control information for service features of a telephone switching system.
In telephone switching systems, desired numbers can be entered either by means of rotary dials or through numeric keypads.
The following assumes that modern numeric keypad and multifrequency signalling are used in the system.
When the handset of a telephone station is removed, the station is connected to a multifrequency code receiver through a line circuit and a switching network. The sequence of digits of a desired number or for a service feature of the telephone switching system, entered through the numeric keypad, is detected in the multifrequency code receiver, converted into corresponding control signals, and transmitted to a switching control unit of the telephone switching system for further establishment of the connection.
Although the subscriber can rapidly enter even long numbers, call up numbers stored in the abbreviated-dialling facility, or activate service features, such as call forwarding or "camp-on busy" in a private branch exchange, there is the big disadvantage that he can use these services only by entering a large number of different sequences of digits.
The subscriber is thus compelled to either remember those sequences of digits or look them up in a list. In addition, in a conventional telephone switching system, he must be able to distinguish between many different tones, such as busy tone, ringing tone, etc.